A retarder is an auxiliary safety device for braking a vehicle. The retarder applies a braking force on the transmission component of the vehicle and plays a role in reducing the running speed of the vehicle. At present, the retarders most widely in use in China are eddy current retarders. Eddy current retarders convert the kinetic energy of running vehicles into thermal energy according to electromagnetic principle and radiate heat by means of air cooling. Eddy current retarders can improve the braking performance of automobiles, eliminate the noise and environmental pollution associated with conventional brakes, lengthen the service lifetime of brake pads and tires, and greatly improve the safety, comfort and economy of automobiles. Although an eddy current retarder has a number of advantages including a simple structure, low production and manufacturing cost, a short response time, intelligent control of braking torque and so on, it tends to have a large volume and weight, high power consumption, poor heat dissipation, and serious decay of braking torque during continuous operation. On the basis of the braking principle of an eddy current retarder, a self-generating system is added to a self-excited retarder and directly supplies power to the retarder so that there is no need to increase the capacity of the generator or battery of the automobile. It is light, energy efficient and environmentally friendly.
Existing self-excited retarders typically comprise a stator with exciting winding, a rotor with an air channel, and a generating system. The rotor is disposed on the automotive transmission system. The rotor coil is fixed on the chassis. The generating system typically comprises a three-phase synchronous generator and a rectifier circuit. When the generating system is started, the generator supplies power to the retarder, the stator coil is energized, magnetic lines of force pass the rotor, the self-excited retarder is in a braking state, and the kinetic energy of the automobile is converted into thermal energy and then dissipated to the atmosphere through the rotating rotor. When the generating system is shut down, no electric current passes through the stator coil, and the self-excited retarder is in a non-braking state. This structure has the advantage of power conservation, but the thermal decay of braking torque during continuous operation is still a serious issue.
The invention patent titled “Double-Rotor Self-Excited Retarder and Control Method Thereof” (Chinese Patent Application No. 201010516737.0) and the utility model patent titled “Automobile Retarder with Self-Generating Function” (Chinese Patent Application No. 201020205726.6) both disclose a self-excited retarder that is air cooled for heat dissipation, which cannot effectively dissipate the heat generated on the eddy current inductors of the retarders. This limits the increase of the braking torque of the self-excited retarders and the duration of continuous braking. The invention patent titled “A Self-Excited Retarder with A Cooling System” (Chinese Patent Application No. 200810243194.2) discloses a self-excited retarder, which dissipates heat by means of water cooling. Although the problem of water dissipation is addressed, this design requires a brush gear in order to transfer the power on the stator armature of the generator to the rotor coil of the rotating retarder. Consequently, the useful life is relatively short.